The present invention is related to processes and apparatuses for making strong, soft, absorbent fibrous webs. More particularly, the present invention is concerned with foreshortened fibrous webs.
Fibrous structures, such as paper webs, are produced by a variety of processes. For example, paper webs may be produced according to commonly-assigned U.S. Pat. Nos.: 5,556,509, issued Sep. 17, 1996 to Trokhan et al.; 5,580,423, issued Dec. 3, 1996 to Ampulski et al.; 5,609,725, issued Mar. 11, 1997 to Phan; 5,629,052, issued May 13, 1997 to Trokhan et al.; 5,637,194, issued Jun. 10, 1997 to Ampulski et al.; and 5,674,663, issued Oct. 7, 1997 to McFarland et al., the disclosures of which are incorporated herein by reference. Paper webs may also be made using through-air drying processes as described in commonly-assigned U.S. Pat. Nos. 4,514,345, issued Apr. 30, 1985 to Johnson et al.; 4,528,239, issued July 9 to Trokhan, 1985; 4,529,480, issued Jul. 16, 1985 to Trokhan; 4,637,859, issued Jan. 20, 1987 to Trokhan; and 5,334,289, issued Aug. 2, 1994 to Trokhan et al. The disclosures of the foregoing patents are incorporated herein by reference.
Foreshortening of a fibrous webs may be used to increase the web""s caliper, absorbency and softness. Foreshortening refers to reduction in length of a dry web, resulting from application of energy to the web. Typically, during foreshortening, rearrangement of the fibers in the web occurs, accompanied by at least partial disruption of fiber-to-fiber bonds. As a result of foreshortening, micro-folds, commonly called xe2x80x9ccrepexe2x80x9d are formed in the web.
It has been discovered that the increase in caliper, or bulk, of the foreshortened web may further be achieved by relaxing, at least partially, the crepe in the web. It has been further found that the crepe can be relaxed in pre-selected portions of the web such that the rest of the web, not affected by the crepe relaxation, retains the quality of the foreshortened web.
Accordingly, it is a subject of the present invention to provide a novel process for increasing bulk of the foreshortened web by relaxing the web""s crepe in the selected portions of the web. It is another object of the present invention to provide an apparatus for increasing bulk of the foreshortened web by relaxing the web""s crepe in the selected portions of the web.
The present invention provides a process and an apparatus for increasing caliper/bulk of a foreshortened fibrous web by causing selected micro-regions, or portions, of the foreshortened web to relax crepe therein, thereby expanding outwardly from the general plan of the web. The process comprises the steps of providing a foreshortened web comprising crepe and having a general plane; and adding moisture to the web or to at least the web""s selected portions, thereby causing relaxation of the crepe in the selected portions and their expansion outwardly from the general plane of the web, while retaining the crepe in the rest of the web. The preferred apparatus comprises two mutually opposite surfaces designed to receive and restrain the foreshortened web therebetween, at least one of the surfaces having a plurality of fluid-permeable expansion conduits therethrough; a means for moistening the web or at least its selected portions corresponding to the expansion conduits when the foreshortened web is disposed between the two surfaces; and a means for creating a temperature differential between the two surfaces such that when the web is restrained between the surfaces, the temperature differential is sufficient to cause the moisture added to the web to move through the web in the direction from one surface toward the other, thereby relaxing crepe in the selected portions of the web and causing the selected portions to expand through the expansion conduits.
A first step of the process of the present invention comprises providing a foreshortened, and preferably fibrous, web. The term xe2x80x9cforeshortenedxe2x80x9d web refers to a web which has been reduced in length, i.e., substantially proportionally contracted along its length, in a machine direction. The first step of providing a fibrous web may be preceded by the steps of forming such a web and then foreshortening the web. The fibrous web suitable for the present invention may be made by any papermaking process known in the art, including, but not limited to, a conventional process and a through-air drying process. The present invention also contemplates the use of the web that has been rewetted prior to being foreshortened. The foreshortened web is generally characterized by a plurality of micro-folds running across the web""s length, which is known in the art as xe2x80x9ccrepe.xe2x80x9d Foreshortening may be accomplished by any method known in the art, for example, by creping, by transferring the web from the first press surface to a slower-moving transfer fabric, or by the combination thereof.
Preferably, the foreshortened web is disposed on a working surface. The preferred working surface has a plurality of fluid-permeable expansion conduits therethrough. One preferred working surface is formed by a belt comprising a (preferably resinous) framework joined to a fluid-permeable reinforcing structure and protruding outwardly from the reinforcing structure, thereby forming the network area. The framework may comprise an essentially continuous and macroscopically monoplanar network area, in which case the plurality of expansion conduits preferably comprises a plurality of discrete orifices, or holes, which are dispersed throughout and encompassed by the continuous network area of the working surface. Alternatively or additionally, the work surface may comprise a plurality of discrete areas formed by discrete protrusions extending from the reinforcing structure, in which case an essentially continuous expansion conduit encompasses the plurality of discrete protrusions.
Preferably, the expansion conduits and/or protrusions are arranged in a pre-selected pattern, and more preferably, the pattern of the arrangement of the expansion conduits and/or protrusions is non-random and repeating. If the patterned working surface comprises discrete areas formed by the individual protrusions, the work surface""s discrete areas may have the discrete expansion conduits therethrough, analogous to the discrete expansion conduits in the continuous work surface. The working surface may comprise a surface of a fluid-permeable platen orxe2x80x94in a preferred continuous processxe2x80x94a fluid-permeable endless belt or band capable of traveling in a machine direction.
The steps of disposing the foreshortened web on the working surface and moistening the web may be performed either sequentially or simultaneously. If the dry foreshortened web is being first disposed on the working surface, the moisture can subsequently be added to the web disposed on the working surface. Various means may be used for moistening the foreshortened web, such as, for example, spraying the web with water or penetrating the web by steam under pressure. A plurality of jets discharging water onto the selected portions of the web according to a pre-determined pattern may also be used. Preferably, the web, or its selected portions, is/are moistened to have a moisture content from about 95% to about 25%, i.e., the web""s preferred fiber-consistency is from about 5% to about 75%. More preferably, the moisture content of the selected portions of the web, after they have been moistened, is from 85% to 35%, i.e., the web""s more preferred fiber-consistency is from about 15% to about 65%.
The moisture may be added primarily to the selected portions of the foreshortened web, i.e., those portions which correspond to the expansion conduits of the working surface, and which are not in direct and immediate contact with the working surface. The moisture is added to the selected portions of the web preferably after or simultaneously with the step of disposing the web on the working surface. The moisture added to the web may comprise such functional papermaking additives as softeners and debonders, including, but not limited to, lotions, perfumes, anti-microbial agents, wet-strength resin, etc.
Under the influence of the moisture added, the web""s selected portions relax the crepe therein and consequently expand outwardly from the general plane of the web, thus increasing bulk of the web. At the same time, the rest of the web, comprising surface-contacting portions which are in direct and immediate contact with the working surface, retains the crepe therein. The resulting web structure comprises, therefore, at least two distinct regions: a region formed by the web""s previously foreshortened portion which has retained the crepe therein, and a region comprising the crepe-relaxed portion having increased (relative to the previously foreshortened portion) caliper. Each of the regions may be substantially continuous, or may comprise a plurality of discrete micro-regions, or a combination thereof. Preferably, the crepe-relaxed portion comprises a plurality of discrete domes outwardly extending from the plane formed by the foreshortened portions of the web. The domes may extend from one side of the web, or from both opposite sides of the web.
One way of retaining crepe in the surface-contacting portions of the foreshortened web comprises adhering the surface-contacting portions to the working surface such as to prevent lateral movement of the surface-contacting portions relative to the working surface with which they are in contact. To accomplish this, the working surface can be treated with an adhesive material, such as, for example, creping adhesive. Alternatively or additionally, the working surface can comprise asperities thereon, preventing the lateral movement of the surface-contacting portions. Other means of creating a sufficient friction between the working surface and the surface-contacting portions of the foreshortened web may be employed to prevent the lateral movement of the surface-contacting portions relative to the working surface.
In the preferred embodiment of the process and the apparatus, a pressing surface, opposite to and facing the working surface, is provided. The pressing surface is a surface adapted to impress the foreshortened web against the working surface. The foreshortened web is constrained, or impressed, between the working and pressing surfaces to the extent necessary to prevent (or contain if desired) expansion of those portions of the web which do not correspond to the expansion conduits. Those portions (defined herein as xe2x80x9csurface-contacting portionsxe2x80x9d) retain the crepe therein, while the selected portions of the web are free to expand through the expansion conduits.
The pressing surface may comprise an essentially flat area, or it may have projected areas. The projected areas may comprise continuous network area, or discrete areas, or a combination thereof. Pressing surface may also have expansion conduits therethrough, similar to those of the working surface. The expansion conduits of the pressing surface can correspond to the expansion conduits of the working surface. In the latter instance, the moisture (water and/or steam) can be delivered to and removed from the web using corresponding expansion conduits of the pressing and working surfaces. The latter embodiment provides an additional benefit of allowing the selected portions expand in both opposite directionsxe2x80x94through the expansion conduits of the working surface and through the expansion conduits of the pressing surface. In another embodiment, the pressing surface""s conduits do not correspond to the working surface""s conduits. In this instance some of the selected portions of the web can expand only through the pressing surface""s conduits, while the other selected portions can expand only through the working surface""s conduits. The last two embodiments of the process and the apparatus allow one to create structured patterned webs.
Preferably, the working surface is associated with a supporting surface such that the working surface having the web thereon is juxtaposed between the pressing surface (contacting the web) and the supporting surface. In the preferred embodiment of the apparatus and the process of the present invention, a temperature differential of at least 50xc2x0 F. is created between the pressing surface and the supporting surface. Preferably, but not necessarily, the pressing surface has a relatively higher temperature, and the supporting surface has a relatively lower temperature. The preferred temperature differential is at least 50xc2x0 F., and the more preferred temperature differential is at least 100xc2x0 F. A preferred temperature of the xe2x80x9ccoldxe2x80x9d surface is less than 212xc2x0 F. The temperature differential drives the moisture added to the web through the web""s selected portions thereby relaxing the crepe in the selected portions and causing the selected portions to expand through the expansion conduits. To accumulate the moisture driven through the web, a fluid-permeable fabric is juxtaposed between the xe2x80x9ccoldxe2x80x9d (preferably working) surface and the xe2x80x9chotxe2x80x9d (preferably supporting) surface. The fabric should have a void volume sufficient to accumulate the moisture condensing thereinto. This process or any other process known in the art may be used to dry the web.
In one preferred embodiment, the pressing surface comprises a surface of a sintered layer capable of retaining sufficient volume of moisture. The preferred sintered layer comprises metal woven belt capable of containing a sufficient volume of moisture therein and to release the moisture under the influence of the temperature differential. The metal is preferred for its superior heat-transfer properties. When the web and the working surface are impressed between the pressing and supporting surfaces, the moisture contained in the sintered layer moves into and through the web and towards the supporting surface. The crepe in the surface-contacting portions of the web, which are sufficiently contained between the pressing surface and the working surface, is not affected (or affected to a lower degree, if desired) by the water driven through the web from the pressing surface towards the supporting surface. The web""s selected areas, which correspond to the expansion conduits of the working surface and/or the pressing surface, are not sufficiently contained between the pressing surface and the working surface, due to the existence of the expansion conduits in both or one of the surfaces. Therefore, the selected portions are not prevented from expanding through the expansion conduits (or prevented to a significantly lower degree relative to the surface-contacting portions). The expanded selected portions of the web form xe2x80x9cdomesxe2x80x9d of a finished product, thereby increasing the bulk or overall caliper of the finished web.
In one of the embodiments of the preferred continuous process of the present invention, each of the pressing surface and the working surface is formed by an endless belt or band traveling in the machine direction. An endless condensation belt (fabric) traveling in the machine direction and capable of receiving a sufficient amount of the condensed moisture is disposed between the supporting surface and the working surface. The moisture which is driven through the selected portions of the web and through the expansion conduits of the working surface condenses into the fabric disposed between the working surface and the supporting surface. A means for collecting and recycling the moisture, well known in the art, may be used in the process of the present invention.
The portions which are impressed between the working surface and the pressing surface may be further densified, if desired. The selected portions of the web corresponding to the expansion conduits are not densified, or densified (if desired) to a lesser degree than the impressed portions are. In the latter instance, a pressure differential may be controlled, on the one handxe2x80x94by the distance between the pressing surface and the corresponding working surface, and on the other handxe2x80x94by the distance between the pressing surface and a surface restricting the expansion of the selected portions.
In the pressing surface comprising projected areas, some of the projected areas may be registered (either in a knob-to-knob pattern, or in a nested pattern, or in a pattern comprising a combination thereof) with the working surface when the web is impressed between the pressing surface and the working surface. The embodiment of the apparatus is contemplated, in which only some of the projected areas of the pressing surface have corresponding projected areas of the working surface. Thus, some of the selected portions of the web may be partially restrained, in the direction perpendicular to the working surface, to a lesser degree relative to the portions impressed between the working surface and the pressing surface. Consequently, it is believed that the selected portions of the web may comprise in the latter instance sub-portions which are relatively unconstrained in the direction perpendicular to the working surface, and sub-portions which are relatively constrained and may be partially impressed (and therefore possibly densified) by the pressing surface""s projected areas corresponding to the expansion conduits of the working surface. Such an arrangement of the working surface and the pressing surface may beneficially produce a web having at least three differential micro-regions: first micro-regions formed by the portions constrained in the direction perpendicular to the working surface and thus substantially retaining the crepe therein; second micro-regions formed by the sub-portions partially-constrained in the direction perpendicular to the working surface and thus having crepe partially relaxed, the second micro-regions partially expanding in the direction perpendicular to the working surface; and the third micro-regions formed by the sub-portions relatively unconstrained in the direction perpendicular to the working surface. having crepe substantially relaxed therein, the third micro-regions expending in the direction perpendicular to the working surface.
The expansion of the selected areas may be assisted by deflecting, under pressure, the moistened selected portions of the web through the expansion conduits. Vacuum or differential pressure can be used as a means for deflecting the selected portions through the expansion conduits. The means for deflecting may also comprise steam or water moving, preferably under pressure, through the selected portions and through the expansion conduits. A combination of steam and water as means for deflecting is also contemplated in the present invention. The pressing surface""s projected areas corresponding to the expansion conduits of the working surface can also comprise the means for deflecting the selected portions of the web. In one exemplary embodiment, the projected areas of the pressing surface correspond to the expansion conduits of the working surface and are in contact with the selected portions of the web. When the web is constrained between the pressing surface and the working surface, the projected areas of the pressing surface push the selected portions of the web through the expansion conduits of the working surface, thereby facilitating the expansion of the selected portions.
xe2x80x9cAngledxe2x80x9d expansion of the selected portions is also contemplated by the present invention. In this instance, the selected portions of the web are caused to expand to form an xe2x80x9cangledxe2x80x9d position relative to the plane of the belt, i.e., the axes of at least some of the domes formed by the selected portions and the working surface form acute angles therebetween. The working surface may comprise a plurality of protuberances, at least some of which are angled relative to the working surface, i.e., the axes of the protuberances and the working surface form acute angles therebetween. Than, the selected portions of the web, while expanding through the expansion conduits, will take the xe2x80x9cangledxe2x80x9d position relative to the working surface, and the final web product will have the xe2x80x9cangledxe2x80x9d continuous domes, i.e., the continuous domes cross-sectional axes of which form acute angles with the general plan of the web.
The web having the crepe relaxed in the selected portions may be re-foreshortened by, for example, adhering the crepe-relaxed and expanded selected portions of the web to the creping surface and then creping therefrom with a doctor blade.